Synthetic glycoconjugates as experimental vaccines Shigella dysenteriae type 1 causes dysentery/shigellosis in all age groups especially in young children. It may be both endemic and epidemic.There is evidence that shigellosis causes stunted growth of children in the developing world. Because this bacterium has acquired resistance to most of the available antibiotics, mass vaccination in the afflicted area would be the best long-term solution. However, there is no licensed shigella vaccine. There is evidence that IgG antibodies to the O-specific polysaccharide (O-SP) protects the host. The O-SP S. dysentheriae type 1 consists of a linear chain of the 3)-alpha-RHAp-(1,2)-alpha-GALp-(1,3)-alpha-GLCNACp-(1,3)-RHAp-(1 tetrasaccharide repeating unit. We demonstrated that BSA conjugates of synthetic octa- to hexadecasaccharide fragments of the O-SP elicit O-SP specific IgG antibodies in mice. The highest antibody levels were obtained with the deca and undecasaccharide-BSA conjugates where the non-reducing terminal residue was either N-acetyl-glucosamine or galactose. Having established the optimal structure for the saccharide region, we prepared sufficient amounts of the saccharides and conjugated them to a genetically modified, non-toxic diphtheria toxin, using the oxime conjugation technology. The clinical lots so obtained will be tested in a phase 1 study. E. coli O148 may cause diseases resembling those caused by S. dysenteriae type 1. It has been proposed that S. dysenteriae type 1 gained its O-SP from E. coli O148;they share the same repeat unit, except that the glucose residue in the E.coli O148 O-SP is replaced by a galactose residue in the S. dysenteriae type 1;both residues having identical alpha anomeric configurations. To analyze the cross-reactivity between these two bacteria, we have synthesized a panel of E. coli O148-related oligosaccharides and their protein conjugates, using the oxime technology. Cross-reactivity was established by the following findings: 1. Antisera raised by either (killed) bacteria or by the E. coli O148 dodecasaccharide-BSA conjugate, bound to the lipopolysaccharides (LPS) of both by immunoblotting. 2. Similarly, antisera raised by killed S. dysenteriae type 1 or by the synthetic type 1 dodecasaccharide-BSA conjugate, bound to both LPSs. 3. The O-SPs of both bacteria inhibited the binding of homologous and heterologous oligosaccharide-protein conjugates induced sera. Based on these findings, we hypothesize that a saccharide-based vaccine against one of these organisms will offer protection against both. Synthetic vaccine against Borrelia burgdorferi B. burgdorferi is a causative agent of Lyme disease that afflicts a large number of people of all ages, including children, in large areas of the US, prominently in the northwestern part of the country. A protein-based vaccine has been approved by the FDA but was withdrawn by the manufacturer. The bacterium expresses two major glycolipids on its surface, termed BBGL-1 and BBGL-2. We have chemically synthesized BBGL-1 and its protein conjugate and showed that both can elicit anti-BBGL-1 antibodies in mice. Our attention has now turned to BBGL-2. It was shown to contain alpha-galactosyl-glycerol, with acyl groups of various chain lengths at two hydroxyls (HO-1 and 2) of the glycerol moiety, e. g. palmitoyl, oleoyl moieties. However, the exact location of the individual fatty acids are not known. To map the probable structure of the individual components we synthesized a number of potential BBGL-2 congeners and tested their ability to bind to anti-B. burgdorferi serum in a dot-blot assay. We found that those that contained palmitoyl groups at both hydroxyls did not bind, independently of the anomeric configuration of the galactose residue or of the configuration of the glycerol moiety. Neither did the one that had a palmitoyl group at the HO-1 position with the H-2 position unacylated. On the other hand those structures that contained two oleolyl groups bound to the anti-B. burgdorferi serum, again, independently of the anomeric configuration of the galactose. These and other findings establish lead structures for the development of a vaccine against B. burgdorferi.